Acclimatization to hypobaric hypoxia of high-altitude (HA) is a complex process. Endocrine changes precede and bring about the necessary physiological changes. Lowlanders exposed to the ‘new’ HA environment also experience psychological changes – a stress that is known to affect plasma hormone concentrations. The aim of the study is to examine: plasma hormone and psychological changes in lowlanders during short- (1-month) and prolonged-stay (6-month) at HA in comparison to sea-level, and with HA-natives at HA. Correlation between psychological variables and plasma hormone levels at HA was also examined. Subjects were male volunteers between 20-50years of age. Lowlanders (n=25) were studied at sea-level, after 1-month stay at ~4500m, and after 6-month stay at ~3600m. HA-natives/Ladakhis (HAN, n=21) were studied at HA only. Psychological tests include: Memory(Digit-symbol); Depression(Beck-Depression-Inventory); Hopelessness(Beck-Hopelessness-scale); Loneliness(UCLA-Loneliness-scale). Plasma hormone levels were measured by enzyme immunoassay/enzyme-linked immunosorbent assay. Short-stay at HA causes changes in certain plasma hormone levels (cortisol, prolactin, T3, fT3, T4) and is associated with depression, loneliness and fear-of-death. Further stay at HA results in an increase in plasma T4. Memory, hopelessness and plasma TSH remain unaffected by HA stress in lowlanders. Variation in plasma hormone levels is present between lowlanders and HAN at HA. However, depression is present in both the groups at HA. Significant correlation was observed between depression/prolactin (r=-0.44); loneliness/freeT3 (r=-0.44) in HAN. The HA environment; rather than psychological factors appear to influence plasma hormone changes in lowlanders at HA. Also, short-stay at HA is associated with emotional stress and major hormone changes.